This disclosure relates, in general, to automated systems for process plants and power plants; and, in particular, relates to an automated drain system and method for servicing a steam flow conduit.
In a process or power plant wherein a two-phase fluid is transferred from one point to another it is important to provide for drainage of any condensate which may occur along the fluid flow path. Particularly, in a power plant in a location upstream from a turbomachine it is important from a potential blade erosion point of view to ensure that any condensate in a fluid delivery header be disposed of by drainage so that water droplets are not entrained in the steam whereupon they may thereafter be carried into the turbomachine. Moreover, it is desirable to immediately remove condensate from a turbomachine casing in order to obviate the possibility of unequal thermal gradients within the turbomachine shell which may thereafter lead to distortion of the turbomachine casing.
One prior art system for effecting automatic drain control is shown and described in U.S. Pat. No. 3,694,103 to Cohen et al. In that patented system load conditions on a turbine are sent through a pressure switch such that drain valve actuation is effected as the turbine load falls to a predetermined level such as 20% of rated load. Thus the drain valves will open at one predetermined set point. While this system may control drain valve position during a drastic change in turbomachine pressure it does not accommodate steam temperature changes at high pressures during which condensation could also occur.
Another prior art system for detecting the occurrence of moisture in a steam conduit is shown in U.S. Pat. No. 4,063,228 to Eggenberger and Miller. That patented system detects the rate of temperature change in a steam conduit in order to detect the presence of moisture. The present invention differs in its approach in that conduit pressure is used to determine a variable set point potential for the occurrence of moisture which is then compared with an actual operating condition.
In accordance with the present invention, a method and system hardware has been developed for an automated drain system which will accurately respond at all combinations of steam temperature and pressure occurring within a steam conduit. The invention has been designed and developed to complement various other automated procedures for power plant start-up and operation. The present invention provides a method and apparatus for an automated drain system which utilizes a variable drain opening and closing set point in accordance with actual sensed conditions within a steam line.
Other objects, advantages and features of the present invention will become apparent from the following description of a preferred embodiment thereof when read in connection with the accompanying drawing.